Traditionally, there have been known techniques for purifying an exhaust gas from a diesel engine by introducing the exhaust gas into an exhaust gas purification device (an exhaust gas aftertreatment device) disposed in an exhaust gas path of the diesel engine, the exhaust gas purification device being constituted by a case internally including a diesel particulate filter (hereinafter, such a case will be referred to as a DPF case) and a case internally including a urea selective reduction catalyst (hereinafter, such a case will be referred to as a selective catalytic reduction (SCR) case) (see, e.g., Patent Literatures 1 and 2 (hereinafter, referred to as PTLs 1 and 2)).